28 Late-Breaking: Standardized ileal digestible histidine to lysine ratio requirement for 7- to 11-kg pigs.

A previous study conducted by our group determined that the standardized ileal digestible (SID) His:Lys ratio requirement for 7- to 11-kg pigs ranged from 29.1 to 29.8%. The objective of this study was to validate the SID His:Lys ratio requirement by creating treatments more closely spaced around the expected requirement. A total of 350 pigs (DNA 600 × 241, initially 6.6 ± 0.36 kg) were used in a 14-d study. There were 10 replicates per treatment and 5 pigs per pen. Pens were blocked by weight and assigned to 1 of 7 dietary treatments containing 24, 28, 30, 32, 34, 36, or 42% SID His:Lys ratios in a randomized complete block design. Dietary SID Lys was 1.25% and all other amino acids met or exceeded the NRC (2012) requirement estimates. Diets were corn, spray-dried whey, and whey protein concentrate-based and treatments were formed by adding crystalline L-His at the expense of corn. Response variables ADG, ADFI, and G:F were fitted using general linear and nonlinear mixed models with heterogeneous variances and pen as the experimental unit. Competing models included quadratic polynomial, broken-line linear, and broken-line quadratic. For each response variable, the best fitting model was selected based on Bayesian Information Criterion. Increasing SID His:Lys ratio resulted in a linear increase (P < 0.01) in ADFI and quadratic responses (P < 0.01) in ADG and G:F. The response for ADFI was not modeled due to its linear nature. The best fitting model for ADG and G:F was the broken-line linear. For ADG, the requirement was estimated at 31.0% SID His:Lys (95% CI: 29.7 to 32.3%). The maximum mean G:F was obtained at 28.6% SID His:Lys (95% CI: 27.1 to 30.0%). In conclusion, the estimated SID His requirement for 7- to 11-kg pigs is no more than 31% of Lys.